U.S. patent number 4,148,141 [Application Number 05/878,719] was granted by the patent office on 1979-04-10 for lawn trimmer cutter head.
This patent grant is currently assigned to Hoffco, Inc.. Invention is credited to Stephen J. Hoff.
United States Patent |
4,148,141 |
Hoff |
April 10, 1979 |
Lawn trimmer cutter head
Abstract
A rotary cutter head for a lawn trimmer or the like has a die
cast head body comprising a top circular wall and a depending hub,
with a plate riveted to the bottom of the hub for forming a spool
to receive a winding of flexible cutting line such as monofilament
nylon. A peripheral depending skirt on the circular wall is
segmented by spaced downward open notches defined at their axial
sides and their tops by convex faces, so as to form line apertures.
A molded bottom glide cup has its cylindrical side wall inside and
spaced from the segmented skirt by a distance less than the line
thickness, with its top edge close below the tops of the notches.
The body is mounted on a drive arbor by a nut seated in and
removable by manual rotation of the glide cup relative to the body.
The cutting line end extends from the winding, over the cup wall
edge, through the top of the notch, and then outward in a free
length which forms the cutting element. Such wall edge and notch
top confine the line to a predetermined plane of rotation, i.e.,
cutting plane, regardless of axially where on the winding the free
length is connected. When the cutting length of the line is worn
and needs renewing, it is pulled down out of the notch and against
the cup side wall and then pulled circumferentially in the space
between that wall and the surrounding segmented skirt to another
notch. The space is narrower than the line thickness and the cup is
made stiff but yieldable to pass the line through the space.
Inventors: |
Hoff; Stephen J. (Richmond,
IN) |
Assignee: |
Hoffco, Inc. (Richmond,
IN)
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Family
ID: |
25372674 |
Appl.
No.: |
05/878,719 |
Filed: |
February 17, 1978 |
Current U.S.
Class: |
30/276;
56/12.7 |
Current CPC
Class: |
A01D
34/416 (20130101) |
Current International
Class: |
A01D
34/416 (20060101); A01D 34/412 (20060101); A01D
035/26 (); A01G 003/06 () |
Field of
Search: |
;30/276,347
;56/12.7,295 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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6919841 |
|
Oct 1969 |
|
DE |
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6938265 |
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Jan 1970 |
|
DE |
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Primary Examiner: Peters; Jimmy C.
Attorney, Agent or Firm: Jenkins, Coffey, Hyland, Badger
& Conrad
Claims
I claim:
1. A rotary cutter head for a lawn trimmer or the like
comprising
a cup-shaped body having a top wall and a depending peripheral
skirt, said skirt containing a series of circumferentially-spaced
downward-open notches,
a bottom cup having a bottom wall spaced from the top wall of the
body and having an upstanding side wall extending toward said top
wall in inside lapping relation with said depending skirt,
the free edge of the side wall being disposed at a level adjacent
the tops of the downward open notches,
means for storing reserve line between the cup-shaped body and
bottom cup, with an end of such line extending from the stored line
to and across the free edge of the bottom cup and thence outward
through the top of a notch, the free edge of the side wall and the
top of the notch confining the extended line for rotation in a
predetermined plane.
2. A rotary cutter head as in claim 1 in which the free edge of the
side wall is spaced axially a short distance below the tops of the
notches so as to define with such notches radially-open
line-passing windows for passage of the cutting line from the
stored line to the extended cutting end.
3. A rotary cutter as in claim 2 in which the tops of the notches
form a rectangular opening defined by convex walls.
4. A rotary cutter head as in claim 1 in which the space between
the free edge of the side wall and the depending skirt is
sufficient to permit the line to be pulled out of its notch and
against the side wall and thence circumferentially between the side
wall and skirt to another notch to lengthen the projecting length
of the line end.
5. A rotary cutter head as in claim 2 in which the space between
the free edge of the side wall and the depending skirt is
sufficient to permit the line to be pulled out of its notch and
against the side wall and thence circumferentially between the side
wall and skirt to another notch to lengthen the projecting length
of the line end.
6. A rotary cutter head as in claim 5 in which the space between
the side wall and the skirt is less than the thickness of the line
and such wall is resiliently yieldable to pass the line through the
space from one notch to another.
7. A rotary cutter head as in claim 5 with the addition of a
flanking plate spaced axially from the top wall of the body and
means extending between such plate and wall to receive a winding of
reserve cutting line.
8. A rotary cutter head as in claim 7 in which said last named
means is a hub integral with the body and the flanking plate is
fixed on such hub.
9. A rotary cutter head as in claim 7 in which the bottom cup is
formed with portions which lie sufficiently close to the bottom
face of the flanking plate at its periphery to prevent escape of
reserve line past such plate.
10. A rotary cutter head as in claim 7 in which the body skirt
extends axially not more than about half the length of the
reserve-line receiving means so as to provide winding clearance,
and said cup side wall extends substantially more than half such
length into lapping relation with the skirt so as to define a
closed storage chamber and retain the reserve line therein.
11. A rotary cutter head as in claim 1 in which the body is formed
with a bore for mounting on a drive shaft, axially separable drive
means between the body and shaft, and a nut engageable with the end
of the shaft, said nut being non-rotatably seated in said bottom
cup and the bottom cup being exposed beyond the skirt for manual
grasping to rotate the cup relative to the body so as to rotate the
nut on and off the shaft.
12. A rotary cutter head for a lawn trimmer or the like
comprising
a first member of inverted cup shape having a top wall and a
depending peripheral skirt which is segmented by a series of
angularly-spaced, downward-open notches,
a second cup-shaped member having a bottom wall and upstanding side
wall, nested in the first member with such side wall extending
inside and in axially-lapping relation with said skirt,
the upper edge of said side wall lying close below the tops of the
notches and therewith defining a peripheral series of line passing
windows, and
means for storing reserve cutting line between said members, with
one end of such line extending through one of said windows as a
free-swinging cutting element.
13. A rotary cutting head as in claim 12 in which there is a radial
space between the skirt and upstanding wall adapted to pass the
line from one notch to another when the end of the line is first
pulled down against the side of the side wall and thence
circumferentially.
14. A rotary cutting head as in claim 12 in which the radial space
between the skirt and upstanding wall is less than the thickness of
the line, and the wall is yieldable to pass the line through such
space.
15. A rotary cutting head for a lawn trimmer or the like
comprising
a body having a top wall, a hub extending axially therefrom,
a retainer on said hub to form with the hub and top wall a
spool-like receptacle for reserve cutting line,
said body also having a peripheral skirt extending axially along
part of the length of the spool so as to leave clearance for
winding the same, at least one downward-open notch in the
peripheral skirt which defines an aperture for the passage of the
free end of the cutting line outward to form a cutting element,
a cup-shaped member removably assembled to said body to enclose
said spool and having an upstanding side wall extending inside said
skirt in lapping relation so as to cross the open lower end of the
notch and retain the line in the closed upper end thereof.
Description
This invention relates to a rotary cutter head for a lawn trimmer
or the like having a cutting element formed by a free-swinging
length of flexible line, such as a length of monofilament nylon
line.
There are a number of implements of this type on the market, from a
number of manufacturers, for use in lawn trimming, edging,
sweeping, clearing, etc. These are exemplified by the Ballas and
Geist U.S. Pat. Nos. 3,708,967; 3,826,068; and 3,859,777, and by
the prior German Gebrauchsmuster or Petty Pat. No. 6,919,841. As
indicated in those patents, an implement of this type presents a
number of problems, and cutter heads of various designs have been
proposed. It is the object of the present invention to provide an
improved cutter head, especially for light-duty work, which is of
relatively simple and inexpensive construction but which provides
highly effective operation and a convenient means of storing
reserve cutting line and of extending such line to renew the
free-swinging length thereof which serves as a cutting element for
the head.
In accordance with the invention, a preferred form of rotary
cutting head comprises an inverted generally cup-shaped body having
a top circular wall, a central depending hub, and a depending
peripheral skirt which is segmented by spaced downward-open
notches. The central hub carries a bottom plate, and such plate and
the top body wall and the hub form a spool to receive a winding of
flexible cutting line such as monofilament nylon. The notches in
the segmented skirt are defined at their axial sides and their tops
by convex faces, so as to form line apertures to pass the cutting
line from the winding outward to a free-swinging cutting end. A
bottom glide cup has its cyclindrical side wall inside and closely
spaced from the segmented skirt, with its top edge close below the
tops of the notches. The body is mounted on a suitable drive shaft
or arbor and held by a nut which may also hold the glide cup in
place. Conveniently, the nut is seated in the glide cup so as to be
removable by manual rotation of the glide cup relative to the
body.
The cutting line extends from the winding on the hub tangentially
and axially as necessary to the upstanding edge of the glide cup,
through the top of the notch, and thence outward in a free length
which forms the cutting element. Such wall edge and notch top
confine the line to a predetermined plane of rotation which
constitutes the cutting plane of the head, regardless of where
along the axial length of the winding the line leaves such winding.
When the cutting length of the line is worn and needs renewing, it
is pulled down out of the notch against the cup side wall, and then
pulled circumferentially in the space between that wall and the
surrounding segmented skirt, to another notch. The space between
the cup wall and the skirt is desirably slightly narrower than the
line thickness, and the glide cup is desirably made of stiff but
somewhat resilient plastics material so that the cup side wall can
flex inward as the line is pulled between it and the overlapping
skirt segment. The top edge of the cup wall is desirably rounded,
and the yieldable wall provides a somewhat resilient support for
the line, especially when the stretch of line between the winding
and that edge extends in a direction which has a substantial axial
component.
The accompanying drawings illustrate the invention and show a
preferred embodiment representing the best mode of carrying out the
invention as presently perceived. In such drawings:
FIG. 1 is a pictorial view showing a lawn trimming implement
carried in a position of use by an operator and fitted with a
cutting head in accordance with the present invention;
FIG. 2 is an axial cross section of a head in accordance with the
invention mounted on a drive arbor at the bottom of the frame shaft
of the implement shown in FIG. 1;
FIG. 3 is a bottom plan view of the head shown in FIG. 2 with parts
broken away; and
FIG. 4 is a fragmental side elevation, from the left of FIGS. 2 and
3.
The implement shown in FIG. 1 comprises a power head 10 from a
lightweight chain saw and a conversion attachment 12 attached
thereto, as more fully disclosed in my copending application Ser.
No. 871,603, filed Jan. 23, 1978. The conversion attachment
comprises a frame shaft tube 14 which extends forward and downward
from the power head 10 and thence through a bend to a generally
vertical lower end 16 on which a rotary cutter head 21 is mounted
for rotation about the axis of the lower shaft end 16. The head 21
is driven by a flexible drive shaft housed within the frame tube 14
and driven through a conversion gear head 18 connected to the power
head 10.
As shown in FIGS. 2 and 3, the head comprises a body 20 having the
general configuration of an inverted shallow cup, with a top radial
wall 22 extending from a hub 24 outward to a depending peripheral
skirt 26. The hub 24 extends downward from the top wall 22 and is
formed with three axially extending spider ribs 26 which together
form the drum portion of a spool to receive a winding 28 of cutting
line 30. One flank of the spool is formed by the top wall 22, and
the opposite or bottom flank is formed by a circular plate 32
fastened against the bottom end face of the hub 24. Conveniently,
the body 20 is a die casting, and the bottom end of the hub is
formed with three integral rivet studs 33 which are riveted over to
hold the plate 32 permanently in place.
The hub 24 is formed with a central bore 34 having a hexagonal or
other non-circular socket 36 at its upper end. The bore and socket
are received over a threaded arbor 38 having a drive nut 40 to
engage the socket 36. The arbor is mounted in a pair of ball
bearings 42 and 44 fixed in a flared portion of the lower end 16 of
the frame tube 14. The top wall 22 of the body 20 desirably carries
a collar 46 standing about the lower edge of the bearing mounting
tube. Such wall may also carry a series of angularly spaced radial
stiffening ribs 48. The outer circumference of the top wall 22
desirably extends a short distance beyond the outer surface of the
segmented skirt 26 to form a bump ring 25 to protect the line from
being pinched between the head and a stationary object.
The skirt 26 of the body 20 extends downward not more than about
half the length of the winding, to leave winding clearance. It is
formed as six cored segments 50 having inner walls 49 and outer
walls 51 and end walls with convex faces 52. The segments 50 are
spaced to define between them notches 54. The notches 54 have
convex vertical side faces, formed by the end faces 52 of the
segments 50. The tops of the arches are formed by surfaces 56 which
are convex in a radial direction as shown in FIG. 2 and straight in
a circumferential direction as shown in FIG. 4. The notches thus
define apertures which are generally rectangular in elevation.
The cutter head also comprises a glide cup 60 having a central hub
portion which forms a retaining seat for a nut 39 threaded onto the
arbor 38 to hold the body 20 and cup 60 together and fixed on the
arbor 38. The glide cup 60 has a rounded bottom wall which forms a
glide surface to support and protect the rotary head as it moves
over the ground in use. The glide cup also has an outer cylindrical
wall 64 which extends axially up inside and inwardly spaced from
the inner face of the skirt 26 so that the two overlap over a
substantial vertical distance.
The bottom of the glide cup 60 is desirably reinforced with a
series of angularly spaced ribs 61 which extend from the hub to the
side wall 62 of that cup. At their outer ends, such ribs 61 have
top lands 63 which lie close below and underlap the periphery of
the plate 32 so as to close the space between the periphery of that
plate 32 and the wall 64 and thereby prevent loose coils of the
line 30 from falling below the plate 32.
As shown in FIG. 4, the top edge 66 of the glide cup 60 lies close
below the top convex surfaces 56 of the notches 54, and such edge
66 and the notch faces 52 and 56 define windows 68 through one of
which the cutting line 30 emerges from the storage space between
the two cups 20 and 60, containing the winding 28 of reserve
cutting line 30. The glide cup edge 66 at the bottom of that window
and the notch top surface 56 at the top of that window define a
predetermined plane of rotation for the free cutting end of the
cutting line 30, and thus define and fix the cutting plane of the
rotary head as the plane between the glide cup edge 66 and the
notch top surfaces 56. As will be obvious from FIG. 2, most of the
reserve line 30 will be stored in the winding 28 at levels outside
that defined cutting plane indicated by the line CP in FIG. 2.
Accordingly, when the line 30 leaves the winding 28 at a level
below the plane CP, as at the point A in FIG. 3, such line will
extend in a tangential plane from the winding 28 as shown in FIG.
3, but will have an upward component of direction in that plane, as
shown in FIG. 2, in order to reach the top edge 66 of the glide cup
60 and to extend outward therefrom through the window 68 in the
predetermined cutting plane CP. To reduce the sharpness of the bend
from the angled portion of the line to that plane, the top edge 66
of the glide cup is desirably rounded.
As is known, in the operation of a device of this type, the
free-swinging end of the line 30, which forms the cutting element
of the head, progressively wears away and must be renewed. The
present invention provides for convenient renewal from the winding
28 of reserve line. To effect such renewal and extend the free end
of the line 30, such free end is manually pulled from its position
in the cutting plane CP downward against the side wall 64 of the
glide cup 60, as indicated by the line 30a shown in dotted lines in
FIG. 2. The line 30a is then pulled circumferentially through the
space between the cylindrical wall 64 of the glide cup 60 and the
inner wall 49 of the adjacent skirt segment 50 to another notch 54
where it is again swung upward to the cutting plane CP. As shown in
FIG. 3, such operation may carry the line 30 from the notch 54a in
the plane of line 2--2, counterclockwise to the next adjacent notch
54b, where the line is shown in dotted lines. This will extend the
line by a substantial increment, depending upon the diameter of the
winding 28. As shown in FIG. 3, this operation carries the point B
on the line 30 shown in full lines to the point B' on the lines
shown in dotted lines.
The head body 20 is desirably an aluminum die casting and the glide
cup a molding of stiff resilient plastics material. The cutting
line used may be any of the plastics lines presently available on
the market, for example, monofilament nylon line. In an
exemplifying embodiment, the head was five inches in diameter, the
line used was nylon monofilament having a diameter of 0.080 inch,
and the freeswinging end forming the cutting element was from five
to seven inches in length. The power head drove the cutting head at
about 4,000 r.p.m.
The head is conveniently assembled as follows: With the glide cup
60 removed from the head body 20, and conveniently with the body
removed from the arbor 38, a reserve length of cutting line 30 is
secured to one of the spider ribs 26 of the hub by passing its end
through a hole 27 in one of the ribs 26 of the hub and then winding
it on the spool formed by the hub and its flanking walls 22 and 32.
The free end of the line is laid in one of the notches with enough
line extending outward to form the cutting element, for example
five to seven inches. The head 20 is then slipped on the arbor 38
and engaged with the drive nut 40, and the glide cup 60, with the
nut 39 seated therein, is threaded onto the end of the arbor 38.
This forms an assembly as shown in the drawings, ready for
use..
In use, rotation of the head causes the free end of the line to
stand out from the head and swing in the cutting plane defined by
the windows 68 between the top edge of the cup wall 64 and the top
portions of the notches 54. Such free-swinging line end forms a
cutting element to perform such operations as lawn trimming and
edging, clearing and sweeping vegetation from around the base of
trees and posts, etc. The plane in which the line swings, i.e. the
cutting plane CP, has a predetermined position axially of the head,
regardless of where along the length of the winding the line leaves
that winding in the stretch leading to the notch 54. The cutting
plane is spaced above the bottom of the drive cup 60 at a favorable
height for lawn trimming operations as the glide cup glides over
the lawn. Also, the bottom portion of the cup is exposed for
grasping by the hand for purposes of tightening and removing the
nut 59, and the side wall of the cup underlaps the skirt of the
head over less than half its freestanding height so that its
underlapping portion can be made stiff but resiliently yieldable
inward from that skirt for purposes of lengthening the cutting
length of line 30 as described above, by moving the free end from
one notch to another.
The spacing between the notches is such that movement of the line
from one notch to the next will lengthen the line by an increment
sufficient to re-establish the desirable cutting length of the
line. In the exemplifying embodiment, such increment was about an
inch and a half, more or less, depending upon the size of the
winding 28 remaining on the hub.
When the line in the winding is used up, it can be readily replaced
by manually rotating the glide cup 60 relative to the head 20 to
remove the nut 39 and the cup, and by winding a fresh length of
line 30 on the spool of the body 20 as before.
The rotary head shown and described is provided with only one free
swinging line 30 forming only a single cutting element. The head is
readily adapted, however, to be provided with a plurality of
cutting elements, up to a total equal to the number of notches in
the skirt of the head. With more cutting elements, it will
ordinarily be desirable to increase the power with which the head
is driven since more cutting elements will increase the work done.
A second cutting element may be provided, for example, by winding
two cutting lines 30 on the spool of the body and then leading the
free end of the second line out through a notch diametrically
opposite from the first line, as indicated by the line 31 shown in
dotted lines in FIG. 3. Each free end will act as a cutting
element, and may be renewed or lengthened in the same way as
described above for the single line.
* * * * *